The invention relates to a method of ascertaining variable characteristic values of high-frequency oscillators. The invention also relates to an apparatus for ascertaining such characteristic values (particularly the damping and/or the resonance frequency) of high-frequency self-oscillating (free-running) oscillators.
Oscillators which embody or are combined with measuring impedances (such as capacitors and/or inductance coils) are used extensively in many fields, for example, in the field of measuring the moisture content of coffee, tobacco, paper and the like. It is also known to vary the damping (and possibly also the resonance frequency) by influencing the impedances so that a determination of changes of damping and/or resonance frequency can result in a determination of changes of moisture content or other parameters of commodities which influence the impedance of the oscillator. Reference may be had, for example, to U.S. Pat. Nos. 2,948,850 and 3,979,581 which disclose high-frequency oscillators with measuring capacitors and wherein the capacitors are influenced by one or more commodities, such as tobacco, coffee, paper, fabric, plastics and/or others, particularly for determination of the moisture content of such commodities. A continuous electric signal is generated as the commodities advance past the capacitor, and such signal is indicative of damping of the capacitor. This signal, together with a signal which corresponds to resonance frequency of the oscillator, can be used for the generation of a signal denoting the moisture content of conveyed commodities. Reference may also be had to U.S. Pat. No. 3,412,856.